Controlled thread tensioner for sewing machines

ABSTRACT

This disclosure relates to a controlled thread tensioner for sewing machines which includes a pair of oppositely movable tension discs, one of which is under the influence of a control bolt, and which control bolt has a portion thereof positioned adjacent a permanent magnet carried by a control shaft of the sewing machine for automatically shifting the position of the control bolt in timed relation to the operation of the sewing machine so as to vary the tension applied to thread by the tension discs.

United States Patent 1191 1111 3,797,426 Von Hagen Mar. 19, 1974 CONTROLLED THREAD TENSIONER FOR 2.698.590 1 1955 Garbe 112/254 SEWING MACHINES 2.7681796 /1956 N 2.938.479 5/1960 Armstead. Jr. 112/254 Inventor: golf-Rudige on Hagen. 3.041.003 6/1962 Oehlschlager et a1. 1. 242/155 R 1 5 rotzingen, Germany 3.6l4.689 10/1971 Canonne 335/219 [73] Assignee: Union Special Maschinenfabrik FOREIGN PATENTS OR APPLICATIONS G.m. -H., tuttgart. rm y 353,970 6/1961 Switzerland 112/254 22 Filed: Mar. 31, 1972 1 Primary Examiner-Jordan Franklin 1] PP 2401208 Assistant Examiner-Peter Nerbun Attorney, Agent, or Firm-Diller, Brown, Ramik 8c [30] Foreign Application Priority Data Wight Apr. 22. 1971 Germany P 2] 19 592.6 ABSTRACT 52 us. (:1. 112/254, 242/ M This 9 relates ccfmmlled threafi tension 51 Int. Cl. D05b 47/04 sewmg machmes Whlch Includes a 0f [58] Field of Search n 1 12/254, 255; 242/150, sitely movable tension discs, one of which is under the 242/150 M 155 M; 335/176 influence of a control bolt, and which control bolt has a portion thereof positioned adjacent a permanent [56] References Cited magnet carried by a control shaft of the sewing ma- UNITED STATES PATENTS chine for automatically shifting the position of the control bolt in timed relation to the operation of the L223??? i; 13;;

sewing machine so as to vary the tension applied to 2611373 10/1952 Aiiifei' iilll'. i 242 150 M EhrQQQb-Y the tension discs 1 2. 650.043 8/1953 I Grein 242/150 M 6 Claims, 5 Drawing Figures CONTROLLED THREAD TENSIONER FOR SEWING MACHINES This invention relates in general to new and useful improvements in sewing machines, and more specifi cally to a controlled thread tensioner for sewing machines. The basic structure of the thread tensioner is conventional and the invention relates to the utilization of a control bolt for varying the relationship between the tension discs so as to vary the tension applied to thread drawn therebetween, the control bolt being at:- tuated by a permanent magnet carried by a control shaft.

BACKGROUND OF THE INVENTION Controlled thread tensioners are well known and several means are provided for effecting the operation thereof. As a rule, the control bolt acting on a movable tension disc is guided radially towards a main shaft of a sewing machine with the tension disc being under pressure from adjustable springs which provide the braking force of the tension discs on the thread. A con trol cam is placed on the main shaft of the sewing machine with the control cam being operable to move the control bolt to counter the force of the spring and thus reduce the thread tension from time to time. Such a construction is disclosed, for example, in the US. patent to Tiesler 2,191,046 granted Feb. 20, 1940.

Thread tensioners controlled in the manner set forth above operate relatively inaccurately since the control bolt is pressed against the control cam only by means of the spring which urge the tension discs together. With increasing machine speed, the spring no longer follows exactly the opening and closing movement of the control bolt. Moreover, the parts of the control bolt and of the control cam rub against each other while subject to a relatively high degree of wear.

In more recent years, the proposal has been made of connecting the control bolt with the armature of an electromagnet and to energize the electromagnet by impulses of a control element placed on the machine shaftsSuch an arrangement is disclosed in the patent to Gilbert Hill, et al., U.S. Pat. No. 2,517,567 granted Aug. 8, I950. Such control arrangements are very expensive. Further, the armature of the electromagnet is also under the influence of a return spring which allows the control. device to become inexact with increasing machine speed.

SUMMARY OF THE INVENTION The present invention is based on the forming of a controlled thread tensioner for sewing machine, which thread tensioner is more simpler in construction and which will react more quickly than those previously available.

In accordance with this invention, the problems of priorthread tensioners have been overcome by providing the control shaftwith a permanent magnet which cooperates either directly with the control bolt or with a ferritic part attached thereto so as to effect a variation in thread tension without there being a physical connection between the control shaft and permanent magnet carried thereby on the one hand and the control bolt or part carried thereby on the other hand.

The permanent magnet forms a circular sector about the control shaft and the part of the control bolt cooperating therewith is dimensioned such that the permanent magnet will act on the control bolt for the desired period of time and will increase the clamping force of the tensioning discs correspondingly. The ferritic part of the control bolt is at a very small distance from the permanent magnet so that the control of the increasing of the clamping force by the tension discs is accomplished without contact.

Preferably, the permanent magnet is embedded in an adjusting ring or collar placed on the control shaft. The control bolt, on the end thereof carrying the tension discs, is connected with a bridge disc which reaches around and through a slider casing encompassing the control bolt. The control bolt itself is screwed into a non-twistable guide shoe. As a result of this connection, the control bolt can be screwed into and out of the guide shoe by turning the slotted casing, as a result of which the shoe shifts radially of the control shaft in order to change the magnetic force produced by the magnetic field with respect to the control bolt.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings:

IN THE DRAWINGS:

FIG. 1 is a sectional view taken through the thread tensioner and shows the relationship thereof with respect to a control shaft of a sewing machine, the sewing machine housing being shown in phantom lines.

FIG. 2 is a side elevational view of the control bolt and the components directly carried thereby.

FIG. 3 is an enlarged vertical sectional view taken along the line 3-3 of FIG. 2 and shows further the de tails of the control bolt and more specifically the bridge discs carried thereby.

FIG. 4 is a fragmentary sectional view similar to FIG. 1 and shows a slightly modified form of means for retaining the normal relationship of the tension discs.

FIG. 5 is a sectional view through the control shaft showing a modified permanent magnet arrangement carried thereby.

Referring now to the drawing in detail, it will be seen that the thread tensioner consists in the customary manner of two tension discs 1,2 which are placed on a slotted end portion of a sleeve 3. The sleeve 3 is inserted in a bore in a mounting sleeve 4 and is held in an adjusted position by means of a set screw 5. The mounting sleeve 4, in turn, is positioned within an eye 6 of a conventional sewing machine housing 7 and is retained in an adjusted position therein by means of a set screw 8.

A control bolt 9'is slidable mounted within the sleeve 3 and on one end thereof there is positioned a bridge disc 11. It is to be noted that adjacent the end thereof, the control bolt 9 is of a reduced section and the bridge disc 11 is provided with a narrow bridge 12 which interlocks with the control bolt 9 so that the bridge disc 11 is movable with the control bolt 9. As is clearly shown in FIG. 3, the bridge disc 11 is also provided with suitable openings which receive the slotted portion of the sleeve 3 so as to interlock the bridge disc with the sleeve 3. The control bolt 9 has the opposite end thereof threaded into a shoe 13 which is positioned within a slot formed in the left-hand face of the mounting sleeve 4, as viewed in FIG. 1 so as to be guided for movement only axially of the control bolt 9. The guide shoe 13, in turn, carries an arcuate disc 14 with the shoe 13, cooperating with the mounting sleeve 4, preventing rotation of the disc 14.

In FIG. 1 there is illustrated a control shaft or main shaft 18 of the sewing machine of which the frame 7 is a part. The shaft 18 has adjustably mounted thereon a mounting ring or collar which carries a permanent magnet 16. The mounting ring 15 is preferably of brass, bronze or other suitable non-magnetizable material. The mounting ring 15 is adjustably clamped on the shaft 18 by means of clamping screws or set screws 17.

The slotted portion of the sleeve 3 which extends beyond the bridge disc 11 is provided with threads and has an enlarged nut 19 threaded thereon followed by a locking nut which locks the nut 19 in an adjusted position relative to the sleeve 3 and permits the rotation of the sleeve 3 and the control bolt 9 upon rotation of the nut 19.

Between the bridge disc 11 and the nut 19 there is a damping member 21 which is preferably in the form of a ring of damping material, for example, rubber. The damping member could consist just as well of a spring, such as is shown in FIG. 4 with the spring being identified by the numeral 22. It is to be understood that a certain constant tension force is imparted to the tension disc by the damping member 21 through the positioning of the nut 19. Y

The primary purpose of the damping member 21 is to serve to supress vibrations of the tension discs 1,2 held against each other. without tension, during operation of the sewing machine.

It will be readily apparent that by twisting the sleeve 3 the control bolt 9 may be rotated through the bridge disc 11 thus changing the relationship of the control bolt 9 with respect to the guide shoe 13. In other words, rotation of the control bolt 9 will result in the shifting of the guide shoe 13 axially of the control bolt and in the illustrated form of the invention shown in FIG. 1, radially in relation to the shaft 18. Through this shifting, the gap between the disc 14 and the outside surface of the permanent magnet 16 can be changed in order to change the clamping power exerted by the permanent magnet on the tension discs 1,2.

It is to be understood that within the scope of the invention, it would be feasible to arrange and to develop the thread tensioner and the permanent magnet in such a way that the disc 14 would be opposite a flat front surface of a rotating part. In this case, the control bolt would naturally run parallel to the axis of the control shaft. However, the embodiment shown in the drawing is particularly advantageous because the shafts of the sewing machines, as a rule, lie parallel to the housing wall and the thread tensioner is disposed perpendicular in relation to the housing wall.

Although only a single permanent magnet 16 has been illustrated in FIG. 1, it has been found that better control of the actuation of the thread tensioner may be obtained by the provision of several such magnets. As is clearly shown in FIG. 5, the shaft 18 may be provided with a mounting ring 23 which differs from the mounting ring 15 in that it is provided with separate sockets for the reception of a plurality of permanent magnets 24. As is indicated by the flux line 25, by utilizing a plurality of smaller permanent magnets in lieu of a single large permanent magnet, the desired circumferential extent of the force field may be obtained with the force field being more uniform throughout the circumferential extent thereof.

Although only preferred embodiments of the thread tensioner have been specifically illustrated and described herein, it is to be understood that minor variations may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims.

I claim:

1. A controlled thread tensioner for sewing machines and like equipment having a rotating control shaft, a pair of opposed cooperating thread tensioning discs, means normally holding said discs in cooperating thread tensioning relation, said means including a pressure control disc, 21 control bolt coupled to said control disc for positioning said control disc and controlling the pressure engagement between said cooperating discs, permanent magnet means carried by said control shaft, and means directly reacted upon by said magnet means once during each revolution of said control shaft directly movable with said control bolt for positioning said control bolt and effecting one tensioning cycle of said cooperating discs per control shaft revolution, said control bolt carrying a magnetic reactive part and positioning the same immediately adjacent the path of said permanent magnet means, and said control bolt including adjusting means for adjusting the spacing between said control disc and said magnetic reactive part to vary the position of said magnetic reactive part relative to said permanent magnet means path and thus vary the clamping effect of said control bolt on said cooperating discs.

2. The thread tensioner of claim 1 wherein said magnetic reactive part includes a guide shoe, and fixed means cooperating with said guide shoe for restricting movement of said guide shoe to movement axially of said control bolt.

3. The thread tensioner of claim 1 wherein said magnetic reactive part includes an arcuate disc closely fitting the path of movement of said permanent magnet means.

4. The thread tensioner of claim 1 wherein said permanent magnet means is supported by a carrier having means circumferentially adjustably mounting said carrier relative to said control shaft.

5. The thread tensioner of claim 1 wherein said control bolt is slidably mounted in a casing, said casing passing through said control disc, and means carried by said casing reacting on said control disc to maintain a normal relationship between said cooperating discs, and movement of said bolt by said permanent magnet means is in a direction to increase the pressure engagement between said cooperating discs.

6. The thread tensioner of claim 1 wherein said permanent magnet means includes at least two circumferentially spaced and cooperating permanent magnets for reacting in unison on said means reacted upon by said magnets and having a magnet field of controlled circumferential extent and of generally uniform magnitude. 

1. A controlled thread tensioner for sewing machines and like equipment having a rotating control shaft, a pair of opposed cooperating thread tensioning discs, means normally holding said discs in cooperating thread tensioning reLation, said means including a pressure control disc, a control bolt coupled to said control disc for positioning said control disc and controlling the pressure engagement between said cooperating discs, permanent magnet means carried by said control shaft, and means directly reacted upon by said magnet means once during each revolution of said control shaft directly movable with said control bolt for positioning said control bolt and effecting one tensioning cycle of said cooperating discs per control shaft revolution, said control bolt carrying a magnetic reactive part and positioning the same immediately adjacent the path of said permanent magnet means, and said control bolt including adjusting means for adjusting the spacing between said control disc and said magnetic reactive part to vary the position of said magnetic reactive part relative to said permanent magnet means path and thus vary the clamping effect of said control bolt on said cooperating discs.
 2. The thread tensioner of claim 1 wherein said magnetic reactive part includes a guide shoe, and fixed means cooperating with said guide shoe for restricting movement of said guide shoe to movement axially of said control bolt.
 3. The thread tensioner of claim 1 wherein said magnetic reactive part includes an arcuate disc closely fitting the path of movement of said permanent magnet means.
 4. The thread tensioner of claim 1 wherein said permanent magnet means is supported by a carrier having means circumferentially adjustably mounting said carrier relative to said control shaft.
 5. The thread tensioner of claim 1 wherein said control bolt is slidably mounted in a casing, said casing passing through said control disc, and means carried by said casing reacting on said control disc to maintain a normal relationship between said cooperating discs, and movement of said bolt by said permanent magnet means is in a direction to increase the pressure engagement between said cooperating discs.
 6. The thread tensioner of claim 1 wherein said permanent magnet means includes at least two circumferentially spaced and cooperating permanent magnets for reacting in unison on said means reacted upon by said magnets and having a magnet field of controlled circumferential extent and of generally uniform magnitude. 